1. Field of the Invention
The present invention is related to centrifugal blood pumps.
2. Description of the Prior Art
Centrifugal pumps have been used for many years to pump a wide variety of different fluid materials. In general, a centrifugal pump includes a pumping chamber with an inlet aligned with a rotational axis of the pump, an outlet adjacent the periphery of the pumping chamber, and an impeller mounted within the pumping chamber for rotation about the axis. The impeller in such pumps can be mounted on a drive shaft which extends outside the pumping chamber to a rotational drive source or the shaft can be mounted within the pumping chamber as a spindle about which the impeller rotates (rotatably driven by means other than the rotation of the shaft, such as a magnetic drive arrangement). In any case, as the impeller is rotated, it imparts centrifugal force and velocity to the fluid, thus pumping the fluid from the pump inlet to the pump outlet.
In recent years, centrifugal pumps have been used extensively for pumping blood during open heart surgery. Examples of centrifugal blood pumps are shown in the following U.S. patents: Rafferty et al U.S. Pat. No. Re. 28,742; Dorman et al U.S. Pat. No. 3,608,088; Rafferty et al U.S. Pat. No. 3,647,324; Kletschka et al U.S. Pat. No. 3,864,055; Rafferty et al U.S. Pat. No. 3,957,389; Rafferty et al U.S. Pat. No. 3,970,408; Rafferty et al U.S. Pat. No. 4,037,984; and Reich et al U.S. Pat. No. 4,135,253.
The pumping of blood requires great care to avoid any damage to the red corpuscles, or any of the other constituents of blood. Any practical blood pump useful as part of heart/lung bypass equipment during open heart surgery must deliver the requisite flow volumes under pressure, without damaging the blood being pumped.
In a centrifugal pump, and in particular in a centrifugal pump for pumping liquids such as blood, a fluid tight seal between the drive shaft and the housing is an important factor in the performance of the pump. Friction at the seal produces heat which can damage both the components of the pump and the blood being pumped if not dissipated.
In prior art centrifugal pumps, the rotation of the impeller can lead to generation of an air bubble surrounding the shaft. This air bubble tends to seek the smallest shaft diameter, which is adjacent the drive shaft seal. In prior art centrifugal pumps, the area adjacent the drive shaft seal has also been a relatively stagnant or low flow area in terms of fluid flow within the pumping chamber. The air bubble tends to insulate the seal from the flow of the fluid within the pump chamber, thus decreasing the dissipation of heat generated by friction at the seal interface.